Rhinoceros, often abbreviated as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to Southern Asia.

Members of the rhinoceros family are characterized by their large size (they are some of the largest remaining megafauna, with all of the species able to reach one tonne or more in weight); as well as by an herbivorous diet; a thick protective skin, 1.5–5 cm thick, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400–600 g); and a large horn. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter, if necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their powerful premolar and molar teeth to grind up plant food.

In the wild, adult rhinoceros have no real natural predators other than humans. Young rhinos can fall prey to predators such as big cats, crocodiles, wild dogs, and hyenas. Although rhinos are large and have a reputation for being tough, they are very easily poached; they visit water holes daily and can be easily killed while they drink. As of December 2009, poaching increased globally while efforts to protect the rhino are considered increasingly ineffective. The worst estimate, that only 3% of poachers are successfully countered, is reported of Zimbabwe. The market for rhino horn is largely supported by practitioners of traditional Chinese medicine which considers the horn effective medicine against fever and even "life saving". Apparently, only Nepal has avoided the crisis, while poachers become more sophisticated. About 69% of Rhino in the world are inhabituated in Nepal. South African officials have called for urgent action against poaching after poachers killed the last female rhino in the Krugersdorp Game Reserve near Johannesburg. Statistics from South African National Parks show a record 333 rhinoceros were killed in 2010.This increased to 668 in 2013.